Half-life

The half-life of radioactive strontium-90 is approximately 29 years. In 1963, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 7 percent of the original amount absorbed remains?

The half-life of radioactive strontium-90 is approximately 29 years. In 1963, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 7 percent of the original amount absorbed remains?